In order to prevent a known type of disease, blood products are routinely exposed to gamma radiation in order to deactivate certain cells. The radiation dose to deactivate these cells is about 2500 to 5000 rads (25-50 Gy). This radiation dose is just below the level where unacceptable damage to other blood components occurs. Because the radiation dose to the blood must be accurately provided, the cylindrical radiation canister, which holds blood bags, must be accurately measured (mapped) in three dimensions using a dosimeter traceable to a known standard.
The prior art dosimeter is described in U.S. Pat. Nos. 5,051,597, issued Sep. 24, 1991, and 5,084,623, issued Jan. 28, 1992.
The prior art dosimeter includes a first ply having indicia thereon, a second ply having a radiation-sensitive zone overlying the indicia of said first ply, said 22 radiation-sensitive zone being capable of changing opacity in response to exposure to a radiation dosage exceeding a predetermined threshold so as to change the visibility of the indicia.
One of the major problems with the prior art dosimeter is that it cannot be used for mapping the dose within the canister.